Though 28(...) later had it right too- if the turning time is so short, they could spread fast too, and the horde would grow. But what i don't get in 28 later, is why arent the zombies figthing among themselves? If they are all mad/raging, they should be fighting all the time! Just when healthy people show up, they could present themselves as more attractive targets...

This might be something similiar to the L4D rage virus, where, once someone is turned, they begin to see non-infected people as horrifying demonic creatures instead of regular people.

Sometimes. At other times I'd wander past a chamber without having gone near it and they were already fighting each other. Scary thought that: zombies with firearms.

As far off canon as they eventually ended up (way to go Capcom) and cheesy/bad-tastic writing the Resident Evil novel series had zombies with firearms. All these years later they are one of the only things I can actually remember from them. Oh, and Jill dropped her car keys in her coffee cup because she was a klutz.

Thinking about armed zombies reminds me of the "Zombie Ninjas" song from the excellent www.songstowearpantsto.com as the chorus starts, "We are ninjas who eat brains. We are zombies who wield swords. We are mostly invisible but we travel in hordes."